Adjective to describe a task that will take a long time because it's a lot of work and/or a lot of waiting

Time-consuming:

It was a time-consuming process, so he hired a professional to do it.

Closer to software:

Time-consuming operations should be run in separate background tasks.

Edit: Android calls them longer-running, meaning CPU-intensive and/or blocking:

A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use. [...] if your service is going to do any CPU intensive (such as MP3 playback) or blocking (such as networking) operations, it should spawn its own thread in which to do that work.

Resource-intensive (1,2) probably is as close a term as is available. Terms like cpu-bound, I/O-bound, and network-bound apply to specific resource-intensive jobs.

When latency is important, consider latency-limited, communication-bound, and non-distributable.

The process of writing Data Transfer and Data Access objects are simple but terribly tedious. And Oh, having to translate existing ones from obsolete HBMs to annotated classes is absolutely horrendous tedium.

tedious [ˈtiːdɪəs]
adj

• Tiresome by reason of length, slowness, or dullness; boring.
• causing fatigue or tedium; monotonous
• Obsolete progressing very slowly

protracted: lasting for a long time or longer than expected or usual. may be an option, or any of its synonyms:

drawn-out

extended

lengthy

prolonged