How Should I Use My 1.5x EXP Coupon?

It's level 30.

I used my 1.5x buff yesterday at warrior grounds and dc'd almost instantly.
Used it today with gold MPE potion + exp accumulation + 10% pendant + 15% merc + 4% guild and I got ~600m exp in 1hr. Half of the time I didn't have the gold potion.

Compared to before, I was getting 1.5b+ exp per hour.

Those stack?? I was using them separately when i trained xenon.

*facepalm*