My math is off on that. A 60 mg vial would last about four weeks at 15 mg per week not four months. A lot of people add more water anyway so they can titrate from 2.5 up to 15 mg over time. Maybe I misread the original point.
If you're into Tirz I'd guess T60 is the one. A month of 15 mg in every jar times ten months. Most folks seem to end up pinning 15 either weekly or so. Any thoughts? When I'm browsing I use T60 for an apples-to-apples comparison.