Cars are getting faster and faster. In the 80's a 15 Second car was fast. In the early 90's 14's were fast. Today you can buy a honda accord v6 and run a high 13 @ 100+ mph completely stock.
My opinion is that a 14 second car is slow, a 13 second car is meh, a 12 second car is decent, an 11 second car is quick and 10's or better is fast.
That said, my 2014 mustang
v6 is the slowest car I've owned since since 2005 and it ran a 13.6 @ 105.2. My opinion is probably skewed a bit on fast vs slow.
99 Chevrolet Camaro Z28 M6 - 6.676 @ 103 in 1/8, 10.512 @ 130.2 on street tires, H/C/I
93 Eagle Talon TSI AWD 5spd - Built 6 Bolt, 16G Evo3, HKS 272 Cams - under construction
94 Mustang GT - 5.0 bored and stroked to 347, Vortech V1 @ 10 PSI, Tremec TKO 600 - PIA