After updating software to andriod 6 the phone become slow and charging draining fast some apps am facing to open it's crashing automatically Can any help me please ..!

When I on hotspot to other person it isstrucking and after connected internet is not working to that mobile or system 

My whatsapp is crashing from evening I reinstalled but still crashing please help me to resolve it

I kept charging from 0 to 100 it took for me to complete 3 hours before the charging completed with in 1hour 20 min  , I went to service center he changed the port but still charging is slow I kept fast charging on Can u please tell me any solution 

Hey guys can some Body help me ! When I am playing game or vidoes or some application when I am using the net will become slow and again it will become high can any Body solve it