Q. Is it good for touring and is it comfortable for long 300 km rides - YZF R15S?

I don't think there is any bike out there to go at a stretch for 300kms long drive, every bike needs rest for both you and bike. As far as R15 is concerned it definitely requires some rest especially for your back,every one and half hr maximum. Engine is definitely smooth and withstand long drives at a stretch,but you need rest. So, in R15, you can definitely go long drives, but you need rests for every hr for safety of your back. If,it really makes a concern go for CBR or even Suzuki gixxer better ride quality and comfort.

It can cruise up to 120kmph all day long I have driven to Leh Ladakh from Mumbai and back covered almost 700 km on first day and I was comfortable ..it is the best bike for solo riders also has the perfect balance of adequate power and good mileage

Depends on the rider my friend. I have been doing long tours since 2016 so for me yes it is comfortable