From what I have read, that is not out of line with the norm for urge drug treatments. The average seems to be cutting down everything by a 1/3 (when it works), so if you were going 15 times, you will probably be going 10 times. If you had 3 accidents a day you will probably have 1-2 accidents a day. Combined with behavioral therapy (Kegels) and bladder training, that could rise from 1/3 to 2/3 reduction in symptoms.
It seems to relate to the base symptoms. Worse symptoms will have less of an affect than those with minimal. After all, 24 down to 16 does not feel like great progress, and 3-6 accidents to 1-3 will also make one feel

Sometimes it can feel like a crap-shoot with the statistics and hoping you fall into the good ones.
Hopefully your new urologist will either be able to adjust the dosage, try you on one of the 7 different drugs of that family, recommend surgery, or give you more information as to the cause of your symptoms. As Patrick also stated, you need to write down your reactions and also some of your other questions to get the max out of each visit.
I agree with Patrick, though. The side affects and inability to 100% move to regular underwear would make me question the value of the drugs in your situation. I hope you gain the insight and help you need.