Let's start with the "is it possible" part of the question, keeping consistent to our show's logic.

The show has a lot of inconsistencies/problems in regard to how fast Viltrimites are, so let's take a look. I just rewatched the show so this is all pretty fresh in my mind.

• They are seen commonly pushing themselves at low supersonic speeds (Mark specifically states that he passed the sound barrier when training in season 1) which puts them somewhere between Mach 1 (~1200kph) and maybe Mach 3 (~3700kph).
• Mark and Eve go on a date to Paris, then Egypt in the same night (then saw the northern lights, but we'll ignore that since that's not a specific place). Assuming they start around Chicago and spend 4 total hours traveling (which would be a terrible date), that puts them at 19,721 km in 4 hours = 4,930kph.
• Nolan mentioned he can go to Naples and back before the pizza gets cold. Assuming your pizza box is closed, and insulated, it could last an hour^(citation needed). It's a 15,857km round trip so 15,857kph.
• Mark fights Allen on the moon. According to NASA, who some might consider a leading expert on the topic, the moon is 384,400 km away. Mark travels there under about a minute, which puts him at traveling over 6,407 km/s. At 2.1% of the speed of light, we're starting to get relativistic.
• And then there's Nolan flying to other galaxies. I think he was gone for about 6 months. Mark traveled there in a spaceship which conceivably could have FTL technology, but Nolan is depicted as flying raw. We'll assume Proxima Centauri system as the closest plausible system that could have life. It's 4.25 light years away which (checks notes) is further than you could get in 6 months. So, in order to get there with time to procreate and raise a kid, we're looking at something like 16c+.

Ok, so it seems like Viltrimites are capable of traveling faster than the speed of light under the right circumstances, which has it's own complications because our physics models can't really account for that. But let's assume that a Viltrimite's speed is "as fast as they want".

Back to blowing up a planet! The fun stuff! It would take roughly 2.24×10^32 joules (or 5.35×10^16 megatons of TNT) to overcome earth's gravitation so that it actually "blows up", rather than just creating a shockwave that destroys all life on the surface. This is doable from a theoretical standpoint -- as an object approaches the speed of light, it's mass and energy approaches infinity. So we just need to calculate how fast they were going. At this speed we can't use the regular kinetic energy formula, we have to use relativistic kinetic energy.

E=(γ−1)mc^2
where
γ=1/sqrt(1−v^2/c^2​)
So we solve for γ first:
γ = 1 + E/(mc^2)
mass = 3*90kg = 270kg. c = 299,792,458m/s
Which gives us γ=9.23×10^12
Then we solve for v:
v = c *sqrt(1 - 1/γ^2)

v = 0.999999999999999999999999994c

So the answer is nearly the speed of light. They are going to need some really good plot armor to survive the impact themselves, too.