I have seen some decent deep space photos done with Dobs, but they usually make up for the need for short exposures with large aperture. On the Obsession telescopes web site they show some photos taken with their various size Dobs at the bottom of the page for the telescope. The 15" is the smallest one they show picures taken by.
Obsession Telescopes / Telescopes / 15" Classic
Equipment: SkyWatcher 12” Collapsible Dob w/Telrad, Explore Scientific 30mm 82*, and 20mm, 14mm, & 9mm 100* EPs, Tele Vue 4X Powermate & Paracorr T2, 2" Lumicon UHC and ND13 (moon) Filters, 2" Astronomik OIII filter, dew heater system, and Nikon Action 7x50 EX Extreme ATB 6.4* binoculars.
I'm enjoying learning the sky by star hopping; just charts, my binoculars, and my Dob!