Would you rather lose -1.5% or -3.6% next month?
First I have to confess to a couple assumptions: the market consensus is that the Federal Reserve Bank ("the Fed") will raise interest rates +0.25% in December. Interest rates are rather low, and the Fed wants them back at "normal" levels. Second assumption: that all bonds will all uniformly move up +0.25%.
Returning to the two bond funds you mentioned, I looked on vanguard.com for these two bond funds, and looked at the "portfolio page". That page has a key number call the bond fund's "duration".
VBLTX, long-term bond, duration 14.6 years
VBTLX, total bond, duration 5.9 years
The impact of changes in bond yields is duration x -1 x change. So:
VBLTX = 14.6 x -1 x 0.25 = -3.6% drop in value when rates rise +0.25%
VBTLX = 5.9 x -1 x 0.25 = -1.5% drop in value when rates rise +0.25%
If you get a lot of increases in bond yields / interest rates, bonds lose value often. We have very low interest rates right now, so this seems more likely. Historical data shows the opposite trend: from the extremely high interest rates of the 1980s to now, rates have been falling and boosting bond values while doing so.