Yup. In some other forums, not discussing the Clarithy PHEV, I've seen complaints that so much of the energy from a L1 charger went to heating the car and/or the battery pack that there was hardly any left over for actually charging the battery, so even after several hours on the charger the car had not gained much EV range.
It does not at all surprise me that this also applies to the Clarity PHEV.
Those who live in mild climates, such as the coastal areas of California, can likely get away with using L1 chargers year-round. But those of use who live in more temperate climates, where it really does get very cold on some wintry days, a L2 charger may be a necessity rather than a luxury.
But as has already been said above, it's best to ask an electrician to check out your home's wiring. Some homes, especially older ones, may need a significant (i.e., expensive) upgrade to the main circuit-breaker box and/or the wiring before a L2 charger can be installed.
And don't be afraid to ask for 2 or 3 estimates. It's amazing how much difference there can be in what different electricians charge... even fully qualified ones.