Hey thanks for playing! I'm working on getting those load times improved. Also the Sniper by default is only usable on a rooftop.
So you need to get either a lock pick or the Rooftop Access card and get withing 50m of a commercial building (colored lighter and slightly yellow on map) then you can get on the roof and setup your sniper at an angle.
I am about to add a new combat card called Overwatch which will be playable with Sniper on the ground. It will let you hold an angle on a specified street at ground level for a certain turn count to set up an ambush.
Appreciate the feedback, I am looking for as much as possible and making updates oftten.