Yes, it is possible that your prescription has changed by that amount.
In addition, your new contact lens brand is very different from the
original brand you wore (it is made with a superior type of plastic).

Give your new trial about a week to adjust to.  It is very common for
someone to have difficulty adjusting to a prescription where the minus
power has been decreased even if they need it.

So your prescription changed, the last one being "a few years ago."
Well, that happens. It's one of the reasons I have a job.

You certainly should go back for a re-check.  If you were given a "trial
pair", that's what that means. You MUST return for follow-up in order to
finalize your prescription prior to ordering lenses.  I would assume you
were told this.

Second point: The new lens is a different design than the former and the
effective power is not necessarily equal. .25 or .50 difference is
certainly possible.

Third point: O2Optix has more than 10 times the oxygen permeability than
the Optima. This might allow a reversal of cornea compression/swelling
and that can easily relate to a .5 difference in power.

Don't be surprised if your Rx changes yet again---in either direction.

--LB, O.D.