I am going to install a 15kw generator with an auto transfer switch to replace a 5kw generator that I had to hand start and manually transfer to a generator panel that had 5, 15 amp ckts. and 3, 20 amp ckts. The new generator panel has the same number of 15 & 20amp ckts. With four additional ckts. For two 240v appliances. The new generator panel will be fed from the main panel with a 70amp breaker. I would like to feed more than just 5, 15amp ckts with the generator. I was sure 15kw would handle more ckts. Can I replace some of the generator 15 amp breakers with the skinny(peanut) type 15 amp breakers so I can have a couple of additional 15 amp circuits?
Thank you, Guy

A generator can handle as many circuits as you like, as long as the load does not exceed 15Kw, or about 60 amps per leg. Installing tandem,or halfsize, breakers will depend on if the generator panel can physically allow them to be installed.

Since your going from a 5Kw to a 15Kw, you already are aware of being careful with what is running during a power failure, so adding a few circuits should not be a problem that you can't handle.