ipad mini wifi problem with ios 9

SO many problems since upgrading to latest ios 9.Thought the update would help but no hasn't changed at all.Connected to wifi but so slow at times ...tried "forget network "...ok for short time..tried "reset network" ...ok for short time .tried "hard reset"..same .tried change dns ..same ...can't downgrade to ios 8 apparently ..but wish I could as had no problems like I have now...Also doesn't matter if I am connected to adsl modem or our mobile internet modem same problems...so not the modem ...Husbands ipad 3 not upgraded to ios 9 has no problems at all ...Any ideas as to what I can try next .