Actually, there 2 ways to get the radio to scan more than 10 talkgroups. This works with other Motorola Trunk radios too.
Method 1:
For each System you setup, set the announcement talkgroup as a talkgroup you want to monitor. If you scan anything in that system, you will hear that talkgroup as well. The only drawback is that you won't see the display change and cannot text tag that talkgroup.
Method 2:
Setup your system and make the announcement talkgroup the same as one of the talkgroups in the system. Now when select that talkgroup, you will hear all the talkgroups in that system. Again, the text tag won't change (the only drawback). You can also program your scan list too, so in addition to the 15 talkgroups in that system, you can scan 10 additional.
If you combine both method's, you can really scan a good number of talkgroups. I have used this method on Maxtrac's, STX's & MTX8000's.