Yes, it is. What do you think a "conservative estimate" means? Here are two definitions for you: "moderate, cautious, low"[1]; "at the lower end of a range of possible numbers"[2].
I was assuming the value being optimized for was runway, so a conservative estimate overshoots on probable fully-loaded cost which results in underestimating how long you have until you die. Overestimating how long until you die has more serious consequences from the perspective of, well, everyone involved.
Arguably if you're talking about spending money then a conservative (i.e. cautious or moderate) estimate is a high estimate.