Please don't take this the wrong way, but I strongly suggest that you not take the word of a friend and certainly not the word of any manufacturer when it comes to which broadhead to use.
That questions is one of the big three questions in the sport of archery that boarders on religious fanaticism.
If you want to start an immediate argument in religion you simply ask a group of people "What is the Best Religion"? If you want to do it in archery, that's one of the easiest ways to do it and everybody has an opinion.
The gentleman who already answered your question is well versed and extremely knowledgeable about this sport, so I'm not going to counter any of the advice he's already provided you with. What I can add are a couple of simple facts that might help you in your search for a head that might suit your needs.
Their are many good broadheads, but just like guns there are different broadheads for different applications, therefore you need to be application specific.
For the TAC15
crossbow you will need to maintain a good F.O.C. (front of center) balancing of your arrows. Between 10 and 15 percent F.O.C. is generally what most professionals will recommend regardless if you're shooting a compound bow or anything else that propels an arrow. This means that you would typically want a broadhead that weighs in around 100 to 110 grains.
Mechanical s are OK if you can find some that won't fly open on the launch, but remember this crossbow has a violent launch cycle that will cause most heads to fly open most of the time, so be careful what you are playing with.
More importantly, it's less important as to if it's a mechanical or a fixed blade head than the design of the head. It's an undeniable fact that a non cut-on-contact broadhead requires 20 percent more energy than a cut on contact broadhead to puncture the hide of a game animal. This means that 20 percent of the stored kinetic energy of your arrow can be lost when using a non-cut-on-contact broadhead. With the TAC15's this is not to big a problem because you also have way more than you need, so you've got plenty to waist without worrying, but for efficiency purposes it's important to understand what the real priorities should be. Fixed blade or mechanical always find and select a good quality Cut-On-Contact style broadhead over all others.
You will never see a Big Game Hunter, such as those hunting African Game animals use anything but a cut-on-contact broadhead. There's a reason for this.
Last, find a broadhead that flies well for you and your weapon and don't worry about what everybody else is using. If you can find a broadhead that flies straight for you and has the other characteristics I just outlined, everybody else is going to wanting to know what broadhead it is that you're using!
Make sure you do some reading on how to tune broadheads to your arrow shafts. This is a critical step in getting good arrow performance. Regardless of what others may tell you, tuning is absolutely necessary to get good arrow to arrow flight performance in archery. It's not as simple as just buying a couple packages of broadheads, screwing them in and being ready to shoot consistent groups at over 50 yards. Just by simply weighing a series of new broadheads would tell you that you have a significant weight difference between the half dozen or dozen new heads. This weight deviation needs to be removed if you want to maintain really good elevation consistency at longer distances.
I hope this helps shed a little light on the real factors one needs to be concerned with instead of the things you typically hear about.