That major service for the 998 engine is actually 14K. BRP specs are to adjust the valves, which means removing the airbox, which takes forever, removing the valve covers and gaskets & replacing the gaskets. Most folks skip the valve adjustment, as it has been found to not necessarily need to be done. Also involves changing the plugs and wires, along with a bunch of other more minor stuff. As you may expect, a LOT of Tupperware has to be removed for this, and that adds to the time. Still, $1600 bucks is really way high. Folks here on SL have gotten it done for half that or less. I got really lucky in that I had it done while my RT was in for the big recall, and they already had it torn apart & it cost me $198.00. I also had them install BajaRon's (he is a site sponsor and a great guy) plugs and wires, since they were going to be changed anyway.
I don't know, someone else here might, if BRP has a flat rate schedule for this service, which would have to be specific to each model. A flat rate is for time, not labor, so prices vary according to what a specific dealer charges per hour. I honestly don't know how long the service takes, but as a hypothetical, say it takes 4 hours and the labor rate is $100/hr, then you are looking at $400.00 plus parts, "shop supplies", whatever that is, and tax. Still gonna be way less than what you were quoted. You might Email BRP and ask them how long the service should take, then find out what the dealer's hourly labor rate is. You can look up parts needed on BRP's site to get prices based on the maintenance schedule in your owner's manual.
Good luck.