On the DB15 the pairs are 1,9 and 3,11
On the RJ45 the pairs are 1,2 and 4,5
Make up 2 adapters, so one will work
DB15 to RJ45
1,9 to 1,2
3,11 to 4,5
then make the reverse
DB15 to RJ45
1,9 to 4,5
3,11 to 1,2
Make a loopback plug to test your equipment.
RJ45 plug
1 to 4
2 to 5