Personally when soloing with VW at your level, I wouldn't use DL or SL on my normal kill rotation, only Curse of Agony, Corr, Immo and/or SB depending on how easy the mobs are to kill. Instead, use every 4th or 5th mob as a battery. Send in VW, put up CoE (if/when you have it), SL and DL to "recharge" yourself, then go back to killing as normal. Also, if you have room to DoT and fear a mob, that's also a good time to DL. Feels like less of a grind when you use different strategies to kill things
You should expect the VW to lose aggro at about 50% mob health, hence my suggested use of SB, which should be on it's way to the mob by the time this happens. If you're at max range, the mob should be dead by the time he gets to you, or near enough that your DoT ticks will finish him off.
Points in the Improved Voidwalker talent do help. I'd also recommend a threat meter such as Omen if you don't have one, so you can see how much headroom you have.