Unit conversions are inconvenient for sure, but I think the worst part is actually fractional length measurements. It may make sense for woodworking and handicraft, which I assume is the origin, but for any other use? Try reading 2 3/16" on an imperial ruler as quickly as 5.6cm. Screw sizes also get affected by this.
As someone who uses imperial measures, it is incredibly fast and easy to read fractional inch measures on a measuring tape or ruler because each fractional unit is half of the previous unit size, and they are marked to differentiate each half size measure from the previous for quick reading. To speed things up I wouldn't count three ticks, I would use a 1/8th tick mark count up one more 1/16th tick.
If you find it difficult, it is merely due to lack of experience in using fractional measures.
