In-game tooltips at 15 points in tree and 852 Ballistic Skill:

The Damage over Time portion deals roughly 66% of the damage of Fragmentation Grenade, an AoE DoT with the same duration.

The Instant Damage portion deals roughly 55% of the damage of Firebomb, your Single Target spammable and Phosphorous Shells, your primary AoE Channel.

The Proposal:
While target is below 50% HP, it ticks at 200% rate, and while below 30% HP, it ticks at 300% rate. Additionally, increase the damage of the ending tick by about 40-50%, putting it's damage at roughly 80-90% of a Firebomb or Phospho tick.
200% rate = Roughly 30% more damage than a Frag Grenade and 7.5 second maximum duration. 300% rate = Roughly double the damage of a Frag Grenade and 5 second maximum duration.
The Reasoning:
The idea of this change is to make the skill perform its intended function much quicker and more reliably: That is, add pressure on a Single Target and then explode for AoE damage. 15 seconds is far too long too wait on a class that already spends far too long developing their damage and the ending damage tick is just too low in my opinion.
It also adds a "soft execute" feature to the Engineer, which is very lacking in finishing power or any real burst in every build, while keeping the theme of Damage over Time.
Considerations:
1. These numbers are just me spit-balling and may not fall exactly in line with what others think is correct, so I would expect testing and revisions.
2. The ability could become quite dangerous if stacked by multiple Engineers, but probably not moreso than those same Engineers all using Snipe on the same target.
3. This same rework should also be applied to Seed of Chaos for Magus.
4. As a 5 point Ability, this could become a key tool for every Engineer/Magus spec. I think this is absolutely fine but I could be wrong.
Thank you and have a great day,
Uchoo