LP earned/lost after every ranked game

I've been playing ranked and winning a lot. I started this season bronze 2 and then got to silver 2 (with my duo). When I win, i get 16/17/18lp but when i lost 1 game, i lost 21lp. op.gg says that my mmr is 1500, so its higher than mmr for silver 2, although i keep getting 16 and losing 21. Is it normal?
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