Yes it is 15kg (wifey not happy as we got 20kg with BMI this year). However my main concern is not the baggage but the fact that they seem to alter their flight times so often. Not good when you have to book your holidays to fit in with work.
I've flown Pegasus once and they were ok - nothing special - I expect Onur to be similar.
At £198 each I was prepared to take the risk it might be Onur - others are asking £250+ for the same dates from Manchester.