my macbook air 2012 now takes too much booting time approx 10-15 min and its too much laggy that i have to wait 5 min for opening an app. it was working fine but when i reinstalled mac os bpressing command+R this problem appeared.

my macbook air 2012 now takes too much booting time approx 10-15 min and its too much laggy that i have to wait 5 min for opening an app. it was working fine but when i reinstalled mac os by pressing command+R this problem appeared. is it a motherboard fault ? A shopkeeper told me that its a motherboard fault. I have replaced its battery .