How closely does the World Trigger anime follow the manga?
It appears that there is little to no major plot differences, with 1 of the 7 story arcs being anime exclusive. However, there are 15 characters exclusive to the anime and 1 area that is exclusive to the anime. Considering that you claim to be at the 2nd Large Scale Invasion part (lasts episodes 22-38 and chapters 44-85), assuming that the second part is halfway through the large scale invasion arc, then you would be around episode 30, doing a simple ratio calculation:

(16 / 2) + 22 episodes = (42 / 2) + 44 chapters;


And you would probably be around Chapter 65 in the manga.

Further Reading:
Here's an article on the Story Arcs
Here's a general article about World Trigger on Wikipedia