You don't say whether she's 25 days fresh or the 25 days is just how long you've been milking her. If she's only 25 days fresh, she'll peak around 45 days. The true test is what she does after that 45 days...if she maintains a nice long lactation curve, or plunges off the face of the earth once her 45 days has passed.
Also, it would help to know how old she is. A first freshener cannot be expected to compete with a fourth or fifth year freshener as that's when they hit prime milk production. And, a sixth-seventh freshener will usually begin to drop in production, so if she's aged...she might not be showing you what her potential was when she was in her prime.
And, as previous posters commented on, if she has kids on the udder, they're not only taking from her, but by incremental feedings, are telling the doe to produce smaller amounts at one time. So, that will skew milk production numbers.
You said you're feeding first cut. Dairy goats require second cut. It's not only more nutritious, but they'll waste less.
And, since milk production is measured in weights, I've converted your 1.5 liters into pounds...I'm terrible with the metric system, but I've figured it to be about 3lbs. Anyone please correct me if I'm wrong. You're milking once a day...and leaving the kid on for the rest or separating them for 12 hours and taking one milking and letting the kid have the other 12 to himself? or are you leaving the kid on for the entire time and taking her in during that time for one milking?
You see there are many variables.
In as far as increasing milk production, first, as I'd mentioned, you should switch her over to second cut. First cut is usually used for non-working, non lactating, animals.
Protein isn't necessarily going to increase milk production, but fat can. Make sure she's getting fat in her diet either by your grain (mine has 4.75% fat) or in the form of BOS or even adding an ounce of corn oil to her daily ration.
Make sure she's not copper deficient or has a large load of parasites as both issues will create an issue with milk production.
Make sure you have a good loose DAIRY mineral salt - don't put blocks out for goats, they need more than they can get from the blocks. Don't use grain or mineral salts intended for both sheep and goats...goats will always lose out as they need much more. They're metabolism is much greater and they require a lot of copper and sheep grain usually doesn't have copper because of sheep's high level of toxicity.
And in conjunction with the loose minerals, make sure she has access to clean fresh water...as water=milk.
In as far as Saanens, if you're here on this forum, you must be interested in making cheese. Sannens might be the holsteins of the goat world, however, in as far as milk production, they are also produce the lowest protein/butterfat which means that you need more Saanen milk to match, pound for pound, that which is required to make cheese made from other breeds. Rarely do you see a Saanen in a cheesemaking goat herd because of that.
Here's ADGA's link to breed averages: http://www.adga.org/index.php?option=com_content&view=article&id=325:arc09breedavg&catid=46:production-testing&Itemid=200
And genetics is key to having a thrifty goat who produces well. I raise registered LaManchas and just recently Nubians and my first fresheners must produce no less than 7-8lbs to remain in the herd. (although if I have FF who is consistently milking a little less but has an excellent lactation curve, I'll keep her on to see how she does the following year) I have some FF who have peaked at 12lbs. I don't have nursing kid issues as I maintain CAE preventative practices and remove the kids from birth and feed them pasteurized milk. That not only ensures a CAE negative herd, but also allows me to effectively gauge each doe's level of production.
All this said, if she's a FF and has a kid or two on the teat and is giving you 3 lbs and your'e feeding her first cut hay...give her a second chance as there are so many variables going on, that it's hard to tell if it's genetic or environmental.
However, if this isn't her first freshening and you start milking her without the interference of nursing kids and she's fed a sufficient balanced diet, and she doesn't pick up...I would get rid of her as it takes just as much time and money to feed and milk a poorly producing animal as it does a good producer.
And, always ask about the milk production of the dam and the sire's dam when purchasing unproven does.
Sorry for the long ramble...but when it comes to dairy goats, I usually have a lot to say. lol