The number of pounds seized increased from 123 to 1518 so the percentage increase is
(1518 - 123)/123 100 = 1134%
I assume this is what you calculated also.
On the other hand
(1518 - 123)/1518 100 = 92%
so you might say "92% of the weight of this year's seizures is an increase over last year." I would however not use this statement as I would expect the question "Do you mean there was a 92% increase over last year?" The answer of course is "No, there was an 1134% increase over last year."
If you want to report the increase in weight of the drugs seized as a percentage increase then you need to use this number, a 1134% increase. You could say that there is more than a ten-fold increase if that sounds better to you. Another option is to report the number of seizures and the percentage increase in the number of seizures rather than use weight. A variable other than weight might be more meaningful, especially if the substantial increase in weight is a consequence of a few large seizures.
Stephen and Penny