What you've found is almost certainly the fastest route to the point you mention. Anything shorter would have to cross from east to west across the southern part of Death Valley National Park, and you can see on the Death Valley Map (PDF) that there is no such road south of CA-190 (not counting a 4WD road that would almost certainly take longer, even if you were equipped to drive it). CA-190 itself is the alternate route shown in your Google Map, which is slightly shorter but has the same predicted travel time (it's probably a narrower, winding road with a lower speed limit).
The area south of Death Valley is occupied by the Fort Irwin army base, so there will be no public roads through there, either. So that leaves you on I-15, which is the route you already found.
(Note that the last part of your route, Forest Road 22S41, is unpaved. See the Forest Service map at http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprd3800325.jpg (caution huge JPEG). Forest Service dirt roads are often in a rather primitive condition - you might need a high clearance 4WD vehicle and off-road driving experience to have a chance of negotiating them successfully. So if you use Google Maps for your navigation, you'll want to pay careful attention to the roads it's suggesting, and their likely condition. For instance, Sherman Pass Road (22S05) is paved, but is also closed all winter. If in doubt, park or forest rangers should have up-to-date information on road conditions.)
As to whether there may be other interesting sequoia groves somewhere else, I don't know.