The Heritage 150 is a great telescope for low-power deep-sky viewing. Its wide field of view and decent aperture make it great for viewing open clusters such as M35, M11, and the Pleiades, or perhaps the Sagittarius Star Cloud.
The brighter nebulae such as Orion, the Swan, and the Lagoon similarly look excellent. With a good UHC or oxygen-III filter you can spot the Veil Nebula. The Dumbbell Nebula looks great with or without a filter, while the Ring and a few other planetary nebulae are visible – albeit pretty small – with the 150P. And of course, the Blinking Planetary will do its trick for you.