15 miles long, 2 miles wide, 1 atmosphere cylinder finished with two half spheres on each end,

steel 7.8 metric tones / m^3
wall thickness 0.5m (calculated minimum strength)

15 miles = 24 000 m
2 miles = 3 200 m

cylinder wall
3.1416*3200 = 10 000
*24000 = 241 000 000
*0.5*7.8 = 941 000 000 tones

two half spheres on each end
1600*1600 = 2 560 000
*4*3.141 = 32 200 000
*0.5*7.8 = 125 000 000 tones

air inside:
1.28 kg/m^3
1600*1600 = 2 560 000
* 24 000 = 61 400 000 000 m^3
*1.28/1000 = 78 600 000 tones

I do not care about half-sphere air.

total weight:
941+125+78.6= 1 140 Mtones
or 1 140 000 000 tones

let's assume 300 tones useful payload per launch
1 140 000 000 / 300 =
= 3 800 000 launches
(24*365.24 = 8 766 hours / year)

433 launches per hour for 1 year
or 43 launches per hour for 10 years
or 14 launches per hour for 30 years
or 4 launches per hour for 100 years

Just to transport such steel-air cylinder in pieces to Earth orbit.

To compare ISS weight is about 400 tones ( 2 850 000 times smaller).

So, showing such technology to do the job ridicule entire issue.
Options depends on available technologies, mass independent gravity fields, other force fields, maybe inside of a celestial body can be maintained habitable and the celestial body can be moved as desired.

Not enough data about which technologies are allowed to be chosen to explore possibilities more.

Thank you for the nice topic but let me recommend James Cameron's Avatar movie (2009), because nobody took consideration about what will happen to current life forms (also intelligent) on Earth2, in case of arrival of savages from Earth1.

Sorry for my English, I hope similar to English language.