Eh i feel like it's been done before. I want a domination style minigame, but this feels too basic. Yeah the quakecraft guns are cool (i do want a minigame with more quake guns), but I feel like this concept is just not original enough. Also 15 to 20 minutes seems way too long, and the game seems slow paced. 10 minutes max, and to make the game more fast paced, give all players jump boost and speed effect like in quakecraft.
Here's my ideas to make this concept more fun and original:
1. Have a certain point on the map in which the team that has it conquered gets their guns or something more powerful.
2. Killstreak mechanics would be cool. For each kill you earn a point, and you can use your points on one time use abilities.
3. A shop like in mob wars would be cool. Instead currency is gotten from conquering areas of the map, and killing other players. The shop would allow the player to buy better guns, or other assorted bonuses, such as regaining health, or temporary team buffs.