Dealing with many consumer-grade laptops and desktops often meant that we would see antivirus solutions that came as a free trial with the machine. The majority of these packages were supplied by Norton or McAfee and were far too intensive for the power of the machine.
Some lower-tier machines, even in 2015, were single core or had very low clock speeds. This meant that the antivirus solution hogged all of the system resources on startup and could then constantly use 30% of the CPU’s resources. The only real solution to this problem was to remove the offending antivirus and install a good free alternative such as Avast which is much less intensive in background use. This was often all the customer would need in terms of protection anyway, with many of the full suites offering services that the customer would never need or even want, in many cases.