Breeding mechanics:
I don't know how you have things set up. Nor do I know which breed of rabbit/hare you have modeled. However looking at only 3 breeds your breeding IS too slow if only barely and only taking into account the number of kits in a litter.
Looking at the facts above is it really unreasonable to set the number of kits at 2 instead of one with different chances for other numbers. For example: once the doe is pregnant you now have a 100% chance of baby rabbits. That then breaks down into a 70% chance for 2, a 18% chance of 1, a 9% chance of 3, and a 3% chance of 4 (determined at conception).
Rabbit Types:
Having seen people mention(complain) that rabbits should at least give fur since they breed so slow; here is a suggestion. Two new types of rabbits only available by breeding the wild rabbits. To be determined at birth with the chances of success as such: 75% normal rabbit. 20% Angora rabbit, and 5% Dwarf rabbit.
1. The Dwarf Rabbit:
2. The Angora rabbit:
edited for spelling mistakes and a forgotten link