What is a normal amount of LP to gain in Diamond

I had stopped playing ranked for a couple seasons ago so this season when I did my placements I was placed in silver, I decided to start playing ranked again and about a month later I am now Diamond 3, I am gaining 15 LP per game, I am concerned that my MMR is lower than it should be due to the fast pace of my climb, what is a normal amount of LP to be gaining in Diamond, and if my LP gains are low what can I do to increase them

Thanks