well there is a huge diffrence between jumping missions and ganking...
- in mission its mostly 1 vs 1-2 Ai+ number of enemies that jump in the mission, but you are unable to get reinforcements, players of your nation are also unable to join you....
- in ganking if you the enemy has a lot more players inside your are able to call in reinforcements and players of your nation are able to join you...
except you wont get reinforcements if your to far away from a friendly port...or if youre near an enemies port... and in your case where you get 15 player behind you... its prob the second one