I've found that ALL games get long-range shooting wrong. Just this year (2017) a Canadian sniper was able to make a kill shot at a mind-blowing 3540m (that's 2.2 miles!) shattering the old record by over 1,000m! So what could a highly trained Star Wars sniper do with a supped up sniper blaster? As long as there's line of sight is there really a range limit? Especially if the GM allows the sniper to spend a Destiny Point to make an impossible shot.
To put it in perspective an average sized man looks like one of those little plastic green army men at 1000 yards.
Star Wars in any of the "rules" I've come across don't really explain why blasters have basically very short range. I mean they call blaster longarms, blaster rifles, even though there's no rifling in the barrel to make it a rifle! I'm not sure why they think the barrel length of a blaster would change it's accuracy either since there's no rifling to being with.
My friends keep telling me "it's just a game" so my advice is do whatever the group thinks is the best outcome for the scene's narrative. With the proper conditions maybe 15 miles can be attained.