Celeron by itself is not the problem. The names "Celeron" and "Pentium" vaguely mean a slower CPU than i3/i5/i7 but by how much, that's not decided by these names. In short: an U or Y after the model number indicates a usable CPU.

If the CPU has a prefix like D,N,Z,J (not G though!) then it's some sort of Atom. These are - in broad terms - crap, especially in single thread performance. A seven year old desktop CPU wipes the floor with the fastest Atom today (of course, the Atom will have a much lower TDP but that doesn't help in itself it's slowness). Typical names are Atom D525, Pentium N3700, Celeron J1900.

If the CPU is called Pentium / Celeron some-number and has a postfix like E, U or Y (E is perhaps embedded, U is ultra low I guess, hell knows what Y is but it's even lower TDP than U) then it's a mobile CPU based on the same technology as i3/i5/i7 and has much better single thread performance and not worse overall performance. Typical names: Celeron 847 (I believe this was the last to actually not have an E/U/Y postfix and only three digits so the naming is different), Celeron 1017U, Pentium 3556U. The number of thousands is the generation: the 847 is Sandy Bridge, Celeron 1xxxU is Ivy Bridge, Pentium 2xxxU means Haswell, the 3556U Broadwell, although the Celeron G39* is Skylake. There is some method to this madness just not much. The Y CPUs for Broadwell and Skylake are called "Core M" not Celeron or Pentium.