PS: Not quite the last ski tour in season 14/15. I did skin up Piz Daint (Ofenpass) in late Mai 2015 on my wy to Bozen, Italy.
The Sustenhorn is one of the easiest to reach “high” ski mountain in early summer. The Sustenpassroad usually only opens in June, so one has to take a 2h drive from Zurich to Steingletscher (1900m). If one wants to extend the tour a the adjacent Gwächtenhorn (3430m) can be climbed first (the East facing slopes soften up earlier than the Northwest facing slopes of the Sustenhorn. If one adds the additional 400m climb to Gwächtenhorn, there is almost 2000m of ascent (and descent).
I went there with Christian Rahn, a fast (!) climber, a week ago. I had a hard time keeping up with him. The snow cover was still sufficient and the downhill snow conditions perfect to about 2500m. PS: This could have been the last ski tour this season.